As is well known in the art, various problems can arise in connection with the storage of various fluids, for example, when a new batch of fluid is introduced into a storage tank holding a previously-introduced batch of fluid. The fluid may be, for instance, crude oil, or other petroleum products.
There may be a need for mixing due to differences between different batches of the same fluid, e.g., differences in composition. When a new volume of fluid is introduced into a tank which already holds a quantity of the fluid, the newly-introduced fluid and the fluid already in the tank may not mix together well, especially if the tank is large. Therefore, it may be important to mix the newly-introduced fluid with the previously-introduced fluid, to achieve homogeneity (or near-homogeneity) of all the fluid in the tank, to an extent. For example, if the fluid is crude oil, there may be differences in the crude oil because of different sources thereof, and it is desirable to mix the crude oil to achieve a degree of homogeneity in the crude oil in the tank.
Typically (although not necessarily), the storage tank has a generally cylindrical footprint. The tank may be relatively small (e.g., as small as about 12 feet (3.6 m.) in diameter) or relatively large (e.g., over 200 (61 m.) or even over 300 (91.4 m.) feet in diameter), and may have a capacity of up to several millions of liters.
Various devices for mixing fluid in storage tanks are known. In general, the conventional mixing devices agitate the fluid, i.e., they introduce additional turbulence into the fluid. In general, in large storage tanks, achieving the desired degree of mixing throughout the fluid in the tank is difficult with a conventional mixer. The problem is compounded by variations in viscosity and other characteristics of the fluid flowing into the tank, as well as variations in the rate of flow of the fluid into the tank. The problem is further compounded by the somewhat difficult environment in which the mixing devices operate, i.e., they typically operate at least partially inside the tank, however, the interior of the tank (and the part of the conventional mixing device positioned therein) is not usually accessible during the operating life of the tank.